PPRuNe Forums - SMOKE from a Singapore 747, Sydney ??

This was around 3pm Sunday Nov 2nd (I think) I was on Coogee beach, Sydney and a 747-3/400 SQ was on finals to runway 25 at Kingsford-Smith Int. The aircraft fly very low, directly above the beach from the north and east when using this runway.
The day was totally clear and sunny, about 26-27 deg C and light westerly winds. I was watching all the planes turn final from base, fly directly over me then dissapear behind me. As this Jumbo was approaching I noticed a line of what looked like 'white smoke' trailing from the rear end of the tail where the APU (Aux power unit) is located.
I have never seen a plane do this and that is why I found it strange. Can anybody give me a clue as to what this could have been please?